JP2010001949A - Roller bearing for ball screw support - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roller bearing for a ball screw support for reducing the weight of a rolling element and improving the fretting resistance, suppressing the damage of a raceway member when the impact load is applied. <P>SOLUTION: A ball 13 of a thrust angular ball bearing 1 for rotatably supporting a screw shaft constituting the ball screw with respect to a housing disposed opposite to the screw shaft is formed of a sintered body comprising, as the main component, a βsialon represented by a compositional formula of Si<SB>6-Z</SB>Al<SB>Z</SB>O<SB>Z</SB>N<SB>8-Z</SB>, satisfying 0.1≤z≤3.5, and impurities as the remainder, and also has a Young's modulus of 180 to 270 GPa. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ball screw supporting rolling bearing, and more particularly to a ball screw supporting rolling bearing provided with a component made of a sintered body containing β sialon as a main component.

  The ball screw includes a screw shaft having a spiral groove formed on the outer peripheral surface, a ball nut having a groove opposed to the screw shaft groove on the inner peripheral surface, and a screw shaft. And a ball which rolls on the groove of the ball nut and is circulated through the inside of the ball nut. Then, by rotating the screw shaft, the ball nut can move in the axial direction of the screw shaft. The screw shaft is rotatably supported by a rolling bearing incorporated in the support unit (see, for example, Patent Document 1).

  Here, the ball bearing supporting rolling bearing incorporated in the support unit is used under the following severe environment. In other words, the ball screw performs a function of linearly moving a member connected to the ball nut, and the ball screw incorporated in the machine device may remain stopped for a relatively long time even during operation of the machine device. is there. Specifically, for example, in a ball screw constituting a table drive mechanism of a machine tool, the ball screw is in a stopped state when the workpiece is processed without moving the workpiece held on the table. It has become. At this time, the ball screw supporting rolling bearing for supporting the screw shaft is subjected to vibration of the machine tool while being stopped. Therefore, fretting may occur in a region where a race member such as a race ring constituting the rolling bearing and a rolling element such as a ball or a roller come into contact with each other. Therefore, improvement in durability against fretting (fretting resistance) is demanded. Further, since the screw shaft of the ball screw as described above may rotate at a high speed, the rolling element for supporting the ball screw that supports the screw shaft is required to reduce the weight of the rolling element.

On the other hand, a rolling element made of silicon nitride may be employed as the rolling element of the ball screw supporting rolling bearing. Since silicon nitride has a smaller specific gravity than steel generally used as a material for the rolling elements, it can contribute to weight reduction of the rolling elements. Further, by adopting silicon nitride as a material for the rolling elements, the race members such as the raceway rings made of steel and the rolling elements such as balls and rollers are made of different materials and the wear resistance of the rolling elements is improved. Therefore, the fretting resistance is also improved. Therefore, by adopting silicon nitride as the material of the rolling element of the ball screw supporting rolling bearing, it is possible to achieve the weight reduction and the improvement of the fretting resistance described above.
JP 2000-104742 A

  On the other hand, an impact load may be applied to the ball screw. For example, in a ball screw constituting a table drive mechanism of a machine tool, troubles such as a collision between the spindle of the machine tool and a table may occur. In such a case, an impact load is applied to the ball bearing supporting rolling bearing.

  Here, silicon nitride has a characteristic that it has a Young's modulus larger than that of steel and is less likely to be elastically deformed. For this reason, the contact area between the rolling element made of silicon nitride and the raceway member is smaller than the rolling element made of steel, and the contact surface pressure tends to increase. For this reason, when a rolling element made of silicon nitride is employed as the rolling element of the ball screw support rolling bearing, if an impact load is applied to the bearing, damage such as indentation is likely to occur on the race member. Damage such as indentations in the raceway member becomes a factor in shortening the life of the ball screw supporting rolling bearing. That is, when a silicon nitride rolling element is used as the rolling element of the ball screw supporting rolling bearing, there is a problem that the raceway member is greatly damaged when an impact load is applied.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a ball screw supporting rolling bearing capable of reducing the weight of the rolling element and improving the fretting resistance while suppressing damage to the raceway member when an impact load is applied. Is to provide.

  The ball screw supporting rolling bearing according to the present invention is a ball screw supporting rolling bearing that rotatably supports a screw shaft constituting the ball screw with respect to a member disposed so as to face the screw shaft. This ball screw supporting rolling bearing includes a race member and a rolling element that contacts the race member and is disposed on an annular raceway. And the rolling element consists of ceramics which can suppress the impact with respect to a track member compared with the case where it consists of silicon nitride. More specifically, for example, the rolling element is made of ceramics having a Young's modulus smaller than that of silicon nitride.

  According to the ball screw supporting rolling bearing of the present invention, even when an impact is applied, damage to the raceway member is suppressed. Therefore, the rolling element is reduced in weight while suppressing damage to the raceway member when an impact load is applied. It is possible to provide a rolling bearing for supporting a ball screw capable of achieving the improvement in the resistance and the fretting resistance.

  A ball screw supporting rolling bearing according to one aspect of the present invention is a ball screw supporting rolling bearing that rotatably supports a screw shaft constituting the ball screw with respect to a member disposed so as to face the screw shaft. is there. This ball screw supporting rolling bearing includes a race member and a rolling element that contacts the race member and is disposed on an annular raceway. And a rolling element is comprised from the sintered compact which has (beta) sialon as a main component and consists of remainder impurities.

  A ball screw supporting rolling bearing according to another aspect of the present invention is a ball screw supporting rolling bearing that rotatably supports a screw shaft constituting the ball screw with respect to a member disposed so as to face the screw shaft. is there. This ball screw supporting rolling bearing includes a race member and a rolling element that contacts the race member and is disposed on an annular raceway. And a rolling element is comprised from the sintered compact which has (beta) sialon as a main component and consists of a remainder sintering auxiliary agent and an impurity.

In the ball screw supporting rolling bearing according to one aspect of the present invention, a β sialon sintered body (sintered body containing β sialon as a main component), which is ceramic, is employed as the rolling element. Therefore, weight reduction of the rolling element and improvement of fretting resistance are achieved. Further, the β sialon sintered body has a Young's modulus smaller than a sintered body made of a general ceramic such as silicon nitride (Si ₃ N ₄ ) or alumina (Al ₂ O ₃ ). Therefore, damage to the raceway member when an impact load is applied can be suppressed. As described above, according to the ball screw supporting rolling bearing of one aspect of the present invention, it is possible to reduce the weight of the rolling element and improve fretting resistance while suppressing damage to the raceway member when an impact load is applied. A ball screw supporting rolling bearing capable of achieving improvement can be provided.

  In addition, the ball screw supporting rolling bearing according to another aspect of the present invention has basically the same configuration as the ball screw supporting rolling bearing according to one aspect of the present invention, and has the same effects. However, the ball screw supporting rolling bearing according to another aspect of the present invention differs from the ball screw supporting rolling bearing according to one aspect of the present invention in that the sintered body contains a sintering aid. According to the ball bearing supporting rolling bearing according to another aspect of the present invention, the use of a sintering aid makes it easy to lower the porosity of the sintered body, and can ensure sufficient durability stably. It is possible to easily provide a rolling bearing for supporting a ball screw.

  As the sintering aid, at least one of magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), rare earth element oxide, nitride, and oxynitride is employed. be able to. In order to achieve the same effect as the ball screw supporting rolling bearing according to one aspect of the present invention, the sintering aid is preferably 20% by mass or less in the sintered body.

Preferably, in the ball screw supporting rolling bearing, the β sialon is represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfies 0.1 ≦ z ≦ 3.5.

  The inventor has investigated in detail the relationship between the rolling fatigue life of a rolling element made of a β sialon sintered body and the composition of β sialon. As a result, the following knowledge was obtained. By adopting a production process including combustion synthesis, β sialon can be produced inexpensively with various compositions having a value of z (hereinafter referred to as z value) of 0.1 or more. In general, the hardness that greatly affects the rolling fatigue life hardly changes in the range of the z value of 4.0 or less that is easy to manufacture. However, when the relationship between the rolling fatigue life of the rolling element made of β sialon sintered body and the z value is investigated in detail, when the z value exceeds 3.5, the rolling fatigue life of the rolling element may decrease. I understood.

  More specifically, when the z value is in the range of 0.1 or more and 3.5 or less, the rolling fatigue life is substantially the same, and if the operation time of the rolling bearing exceeds a predetermined time, the surface of the rolling element is peeled off. Occurs and breaks. On the other hand, if the z value exceeds 3.5, the rolling elements are likely to be worn, resulting in a decrease in the rolling fatigue life. That is, it becomes clear that the failure mode of the rolling element made of β sialon changes with the composition having the z value of 3.5 as a boundary, and the rolling fatigue life decreases when the z value exceeds 3.5. It was. Therefore, in the rolling element made of β sialon sintered body, the z value is preferably set to 3.5 or less in order to ensure a stable and sufficient life. As described above, when the β sialon satisfies 0.1 ≦ z ≦ 3.5, it is possible to provide a ball screw supporting rolling bearing that is inexpensive and excellent in durability.

In the ball screw supporting rolling bearing, preferably, the β sialon is represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfies 0.5 ≦ z ≦ 3.0.

  As a result, the durability of the ball screw supporting rolling bearing when vibration or impact is applied can be further improved.

  In the ball screw supporting rolling bearing, the Young's modulus of the rolling element is preferably 180 GPa or more and 270 GPa or less.

  When the Young's modulus of the rolling element increases, the strength of the material (β sialon sintered body) constituting the rolling element tends to increase. However, when the Young's modulus of the rolling element is increased, the rolling element is less likely to be elastically deformed, so that the contact area with the raceway member is reduced and the contact surface pressure is increased. As a result, the track member is likely to be damaged. On the other hand, when the Young's modulus of the rolling element becomes low, the rolling element is easily elastically deformed, so that the contact area with the raceway member increases and the contact surface pressure decreases. However, on the other hand, when the Young's modulus of the rolling element becomes low, the strength of the material constituting the rolling element tends to decrease. For this reason, the Young's modulus of the rolling element needs to be within a range in which a balance between improvement in the strength of the material constituting the rolling element and reduction in contact surface pressure with the raceway member can be secured.

  More specifically, when the Young's modulus of the rolling element made of β sialon sintered body is less than 180 GPa, the influence of the strength reduction of the material constituting the rolling element exceeds the effect of reducing the contact surface pressure, and the rolling element rolling Dynamic fatigue life is reduced. Further, as the contact area with the raceway member increases, the frictional force acting between the raceway member increases, the bearing torque increases, and the resistance to rotation of the screw shaft increases. Therefore, the Young's modulus of the rolling element made of the β sialon sintered body is preferably 180 GPa or more, and more preferably 220 GPa or more.

  On the other hand, if the Young's modulus of the rolling element made of β sialon sintered body exceeds 270 GPa, the effect of increasing the contact surface pressure exceeds the effect of increasing the strength of the material constituting the rolling element, and the indentation is formed on the rolling surface of the race member. Damage is likely to occur. Therefore, the Young's modulus of the rolling element made of the β sialon sintered body is preferably 270 GPa or less, and more preferably 260 GPa or less.

  In the ball screw supporting rolling bearing, the raceway member may be made of steel. In this case, the surface hardness of the track member is preferably HV680 or more. Thereby, damage to the track member when vibration or impact is applied can be suppressed.

  Preferably, in the ball screw supporting rolling bearing, the rolling element has a dense layer that is a denser layer than the inside in a region including a rolling surface that is a surface in contact with the race member.

  In the rolling element made of the above-described β sialon sintered body, the denseness greatly affects the rolling fatigue life. On the other hand, according to the said structure, a rolling fatigue life improves because the dense layer which is a layer denser than the inside is formed in the area | region containing a rolling surface. As a result, it is possible to provide a ball screw supporting rolling bearing capable of stably ensuring sufficient durability.

  Here, the high-density layer is a layer having a low porosity (high density) in the sintered body, and can be investigated as follows, for example. First, the rolling element is cut in a cross section perpendicular to the surface of the rolling element made of β sialon sintered body, and the cross section is mirror-wrapped. Thereafter, the mirror-wrapped cross section is photographed with oblique light (dark field) of an optical microscope at, for example, about 50 to 100 times and recorded as an image of 300 DPI (Dot Per Inch) or more. At this time, the white region observed as a white region corresponds to a region with high porosity (low density). Therefore, a region where the area ratio of the white region is low is denser than a region where the area ratio is high. The recorded image is binarized using a luminance threshold using an image processing apparatus, and then the area ratio of the white area is measured, and the density of the photographed area can be known from the area ratio. .

  That is, in the ball screw supporting rolling bearing, preferably, the sintered body is formed with a dense layer which is a layer having a lower area ratio in the white region than in the region including the rolling surface. In addition, it is preferable to perform the said imaging | photography at 5 or more places at random, and to evaluate the said area ratio by the average value. Moreover, the area ratio of the said white area | region inside the said sintered compact is 15% or more, for example. In order to further improve the rolling fatigue life of the rolling element made of β sialon sintered body, the dense layer preferably has a thickness of 100 μm or more.

  In the ball screw supporting rolling bearing, preferably, when the cross section of the dense layer is observed with oblique light of an optical microscope, the area ratio of the white region observed as a white region is 7% or less.

  By improving the denseness of the dense layer to such an extent that the area ratio of the white region is 7% or less, the rolling fatigue life of the rolling element made of the β sialon sintered body is further improved. Therefore, with the above configuration, the durability of the ball screw supporting rolling bearing of the present invention can be further improved.

  In the ball screw supporting rolling bearing, preferably, a highly dense layer that is a denser layer than the other regions in the dense layer is formed in the region including the surface of the dense layer.

  By forming a highly dense layer with higher density in the region including the surface of the dense layer, the rolling fatigue resistance of the rolling element made of β sialon sintered body is further improved, and a rolling bearing for ball screw support Can further improve the service life.

  In the ball screw supporting rolling bearing, preferably, when the cross section of the highly dense layer is observed with oblique light of an optical microscope, the area ratio of the white region observed as a white region is 3.5% or less.

  By improving the denseness of the highly dense layer to such an extent that the area ratio of the white region is 3.5% or less, the rolling fatigue life of the rolling element made of the β sialon sintered body is further improved. Therefore, with the above configuration, the durability of the ball screw supporting rolling bearing of the present invention can be further improved.

  As is apparent from the above description, according to the ball bearing supporting rolling bearing of the present invention, it is possible to reduce the weight of the rolling element and to prevent fretting resistance while suppressing damage to the raceway member when an impact load is applied. A ball screw supporting rolling bearing capable of achieving improvement can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a table driving device of a machine tool provided with a ball screw supporting rolling bearing according to an embodiment of the present invention. FIG. 2 is an enlarged schematic sectional view showing the fixed side support unit of FIG. FIG. 3 is an enlarged schematic sectional view of the support side support unit of FIG. With reference to FIGS. 1-3, the table drive device provided with the rolling bearing for ball screw support in one embodiment of this invention is demonstrated.

  Referring to FIG. 1, a table driving device 90 includes a base 94, a screw shaft 91 disposed on the base, a fixed side support unit 92 that supports the screw shaft 91 so as to be rotatable about the axis, and a support side support unit. 93, a ball nut 95 through which the screw shaft 91 passes, a bracket 96 disposed on the ball nut 95, and a table 97 disposed on the ball nut 95 via the bracket 96.

  Referring to FIG. 2, the fixed side support unit 92 includes a pair of thrust angular ball bearings 1, 1 arranged in opposite directions. The thrust angular ball bearing 1 includes an outer ring 11, an inner ring 12 fitted on the outer peripheral surface of the screw shaft 91, and balls 13 as a plurality of rolling elements. Further, the fixed-side support unit 92 is fitted to the outer peripheral surface of the screw shaft 91 so as to contact the inner ring 12, and the sleeve 81 is fitted to the outer peripheral surface of the screw shaft 91 so as to contact the sleeve 81. And a lock nut 82 for fixing the inner ring 12 by tightening in the axial direction. The fixed side support unit 92 includes a housing 83 into which the outer ring 11 is fitted, and a side lid 84 that is fitted into the housing 83 so as to contact the outer ring 11 to fix the outer ring 11 in the axial direction. Thereby, the outer ring 11 is fixed to the housing 83 and the inner ring 12 is fixed to the screw shaft 91. As a result, the screw shaft 91 is supported so as to be rotatable about the axis with respect to the fixed-side support unit 92.

  Furthermore, the sleeve 81 and the side cover on the other side in the axial direction when viewed from the pair of thrust angular ball bearings 1 and between the screw shaft 91 and the housing 83 on the one side in the axial direction as viewed from the pair of thrust angular ball bearings 1. A seal member 85 is disposed between the two and 84. Thereby, intrusion of foreign matters into the bearing and leakage of grease and the like from the bearing can be suppressed.

  On the other hand, referring to FIG. 3, the support side support unit 93 includes a deep groove ball bearing 2 having an outer ring 21, an inner ring 22 and a ball 23, and a housing 86 into which the outer ring 21 is fitted. The inner ring 22 is fitted on the outer periphery of the screw shaft 91. Thereby, the outer ring 21 is fixed to the housing 86 and the inner ring 22 is fixed to the screw shaft 91. As a result, the screw shaft 91 is supported by the support side support unit 93 so as to be rotatable around the shaft.

  That is, the thrust angular contact ball bearing 1 and the deep groove ball bearing 2 rotatably support the screw shaft 91 constituting the ball screw with respect to the housings 83 and 86 that are members disposed so as to face the screw shaft 91. This is a ball screw support rolling bearing.

  Next, the operation of the table driving device 90 will be described. Referring to FIG. 1, when screw shaft 91 that has been rotated by a motor (not shown) rotates, a spiral groove formed on the outer peripheral surface of screw shaft 91 and an inner peripheral surface of ball nut 95 are formed. Multiple balls roll between the treads. Further, the plurality of balls circulate through the inside of the ball nut 95. As a result, the table 97 moves together with the ball nut 95 in the direction of the arrow α (axial direction).

  Next, the thrust angular ball bearing 1 will be described. FIG. 4 is a schematic partial cross-sectional view showing the main part of a thrust angular contact ball bearing as a ball screw supporting rolling bearing in the present embodiment.

  2 and 4, the thrust angular contact ball bearing 1 includes an outer ring 11 as a first race member, an inner ring 12 as a second race member, balls 13 as a plurality of rolling elements, and a cage 14. And. An outer ring rolling surface 11 </ b> A as an annular first rolling surface is formed on the inner peripheral surface of the outer ring 11. On the outer peripheral surface of the inner ring 12, an inner ring rolling surface 12A as an annular second rolling surface facing the outer ring rolling surface 11A is formed. In addition, a plurality of balls 13 is formed with a ball rolling surface 13A (the surface of the ball 13) as a rolling element rolling surface. The balls 13 are in contact with each of the outer ring rolling surface 11A and the inner ring rolling surface 12A on the ball rolling surface 13A, and are arranged at a predetermined pitch in the circumferential direction by an annular retainer 14. It is held so that it can roll on the track. Thereby, the outer ring | wheel 11 and the inner ring | wheel 12 can rotate relatively mutually.

  Here, in the thrust angular contact ball bearing 1, the straight line connecting the contact point between the ball 13 and the outer ring 11 and the contact point between the ball 13 and the inner ring 12 is in the axial direction (the direction of the rotation axis of the thrust angular ball bearing 1). ). Therefore, it is possible to receive not only a load in the axial direction (direction of the rotation axis of the thrust angular ball bearing 1) but also a load in the radial direction, and when a load in the radial direction is applied, A component force is generated. With reference to FIG. 2, in the fixed side support unit 92 of this Embodiment, the said component force is canceled by employ | adopting a pair of thrust angular contact ball bearing 1 arrange | positioned mutually oppositely.

Then, the balls 13 serving as rolling _elements, expressed by a composition formula of _{Si 6-Z Al Z O Z} N 8-Z, as a main component β-sialon satisfying 0.1 ≦ z ≦ 3.5, the balance being impurities The Young's modulus is 180 GPa or more and 270 GPa or less.

  Furthermore, referring to FIG. 4, a ball dense layer 13 </ b> B that is a layer having a higher density than the inside 13 </ b> C is formed in a region including a ball rolling surface 13 </ b> A that is a rolling surface of the ball 13. When the cross section of the dense ball layer 13B is observed with oblique light from an optical microscope, the area ratio of the white region observed as a white region is 7% or less. Therefore, the thrust angular contact ball bearing 1 in the present embodiment can achieve reduction in the weight of the rolling element and improvement in fretting resistance while suppressing damage to the raceway member when an impact load is applied. It is a ball screw support rolling bearing. The impurities include inevitable impurities including those derived from raw materials or those mixed in the manufacturing process.

  Furthermore, referring to FIG. 4, in the region including the ball rolling surface 13 </ b> A that is the surface of the ball dense layer 13 </ b> B, the ball high density that is a layer having a higher density than the other regions in the ball dense layer 13 </ b> B. Layer 13D is formed. When the cross section of the ball height dense layer 13D is observed with oblique light from an optical microscope, the area ratio of the white region observed as a white region is 3.5% or less. Thereby, the durability with respect to the rolling fatigue of the ball 13 is further improved, and the durability of the thrust angular ball bearing 1 is further improved.

  In the present embodiment, the balls 13 constituting the thrust angular ball bearing 1 may be composed of a sintered body mainly composed of β sialon and composed of the remaining sintering aid and impurities. By including a sintering aid, it is easy to reduce the porosity of the sintered body, and the thrust angular contact ball bearing 1 that can stably ensure sufficient durability can be easily provided. The impurities include inevitable impurities including those derived from raw materials or those mixed in the manufacturing process.

  Next, the deep groove ball bearing 2 will be described. FIG. 5 is a schematic partial sectional view showing the main part of a deep groove ball bearing as a ball screw supporting rolling bearing in the present embodiment.

  3 and 5, the deep groove ball bearing 2 basically has the same configuration as the above-mentioned thrust angular ball bearing 1, and has the same effect. That is, the deep groove ball bearing 2 is disposed between an annular outer ring 21 as a race member, an annular inner ring 22 as a race member disposed inside the outer ring 21, and the outer ring 21 and the inner ring 22. And a plurality of balls 23 as rolling elements held by the cage 24. An outer ring rolling surface 21 </ b> A is formed on the inner circumferential surface of the outer ring 21, and an inner ring rolling surface 22 </ b> A is formed on the outer circumferential surface of the inner ring 22. The outer ring 21 and the inner ring 22 are arranged so that the inner ring rolling surface 22A and the outer ring rolling surface 21A face each other. Further, the plurality of balls 23 are in contact with the inner ring rolling surface 22A and the outer ring rolling surface 21A at the ball rolling surface 23A (the surface of the ball 23), and are arranged at a predetermined pitch in the circumferential direction by the cage 14. It is rotatably held on an annular track. With the above configuration, the outer ring 21 and the inner ring 22 of the deep groove ball bearing 2 are rotatable relative to each other.

  4 and 5, the ball 23 constituting the deep groove ball bearing 2 corresponds to the above-described ball 13 and has the same configuration as the inner 13C, the ball dense layer 13B, and the ball height dense layer 13D. It has an inner portion 23C, a ball dense layer 23B, and a ball high dense layer 23D. Therefore, the deep groove ball bearing 2 according to the present embodiment is a ball capable of reducing the weight of the rolling element and improving the fretting resistance while suppressing damage to the raceway member when an impact load is applied. It is a rolling bearing for screw support.

  Next, a method for manufacturing the ball screw supporting rolling bearing in the present embodiment will be described. FIG. 6 is a diagram showing an outline of a method for manufacturing a ball screw supporting rolling bearing according to an embodiment of the present invention. Moreover, FIG. 7 is a figure which shows the outline of the manufacturing method of the rolling element which consists of (beta) sialon sintered compact in one embodiment of this invention.

  Referring to FIG. 6, in the method of manufacturing a ball screw supporting rolling bearing according to the present embodiment, first, a race member manufacturing process for manufacturing a race member and a rolling element manufacturing process for manufacturing a rolling element are performed. The Specifically, in the race member manufacturing process, the outer rings 11, 21 and the inner rings 12, 22 are manufactured. On the other hand, balls 13 and 23 are manufactured in the rolling element manufacturing process.

  And the assembly process of assembling the ball bearing supporting rolling bearing is carried out by combining the track member manufactured in the track member manufacturing process and the rolling element manufactured in the rolling element manufacturing process. Specifically, the thrust angular ball bearing 1 is assembled by combining the outer ring 11 and the inner ring 12 and the ball 13, for example. And a rolling element manufacturing process is implemented using the manufacturing method of the rolling element which consists of the following (beta) sialon sintered compact, for example.

  Referring to FIG. 7, in the method for manufacturing a rolling element made of a β sialon sintered body in the present embodiment, first, a β sialon powder preparation step of preparing β sialon powder is performed. In the β sialon powder preparation step, β sialon powder can be produced at low cost by, for example, a production step employing a combustion synthesis method.

  Next, a mixing step is performed in which a sintering aid is added to and mixed with the β sialon powder prepared in the β sialon powder preparation step. This mixing step can be omitted if no sintering aid is added.

  Next, referring to FIG. 7, a forming step of forming the β sialon powder or a mixture of β sialon powder and a sintering aid into a schematic shape of a rolling element is performed. Specifically, by applying a molding technique such as press molding, cast molding, extrusion molding, rolling granulation, or the like to the above β sialon powder or a mixture of β sialon powder and a sintering aid, the ball 13 , 23 and the like are formed.

  Next, a pre-sintering processing step is performed in which the surface of the molded body is processed so that the molded body is shaped to be closer to the shape of the desired rolling element after sintering. Specifically, by applying a processing method such as green body processing, the molded body is processed to have a shape closer to the shape of the balls 13 and 23 after sintering. This pre-sintering processing step can be omitted if the shape is sufficiently close to the shape of the desired rolling element after sintering at the stage where the molded body is formed in the forming step.

  Next, referring to FIG. 7, a sintering step is performed in which the molded body is sintered. Specifically, the molded body is heated and sintered by a heating method such as heater heating, electromagnetic wave heating by microwaves or millimeter waves under a pressure of 1 MPa or less, for example, so that the balls 13 and 23 are roughly outlined. A sintered body having a shape is produced. Sintering is performed by heating the molded body to a temperature range of 1550 ° C. or higher and 1800 ° C. or lower in an inert gas atmosphere or a mixed gas atmosphere of nitrogen and oxygen. As the inert gas, helium, neon, argon, nitrogen, or the like can be employed, but nitrogen is preferably employed from the viewpoint of reducing manufacturing costs.

  Next, a finishing process for completing the rolling elements is performed by performing a finishing process in which the surface of the sintered body produced in the sintering process is processed and a region including the surface is removed. Specifically, the balls 13, 23 as rolling elements are completed by polishing the surface of the sintered body produced in the sintering step. Through the above steps, the rolling element made of the β sialon sintered body in the present embodiment is completed.

  Here, as a result of sintering in the above-described sintering step, a region having a thickness of about 500 μm from the surface of the sintered body is denser than the inside, and when the cross section is observed with oblique light of an optical microscope, a white region is obtained. A dense layer in which the area ratio of the observed white region is 7% or less is formed. Furthermore, the region having a thickness of about 150 μm from the surface of the sintered body has a higher density than the other regions in the dense layer, and is observed as a white region when the cross section is observed with an oblique light of an optical microscope. A highly dense layer in which the area ratio of the white region is 3.5% or less is formed. Therefore, in the finishing step, it is preferable that the thickness of the sintered body to be removed is 150 μm or less particularly in a region to be a rolling surface. Thereby, a highly dense layer can remain in the region including the ball rolling surfaces 13A and 23A, and the rolling fatigue life of the balls 13 and 23 can be improved.

  The sintering step is preferably performed under a pressure of 0.01 MPa or higher in order to suppress the decomposition of β sialon, and more preferably performed under a pressure of atmospheric pressure or higher in consideration of cost reduction. Moreover, in order to form a dense layer while suppressing manufacturing costs, the sintering process is preferably performed under a pressure of 1 MPa or less. Further, in order to adjust the Young's modulus of the rolling element made of the β sialon sintered body to a desired value of 180 GPa or more and 270 GPa or less, for example, the z value of the β sialon powder prepared in the β sialon powder preparation step is set to 0. What is necessary is just to adjust in the range of 1 <= z <= 3.5. More specifically, the Young's modulus of the β sialon sintered body can be decreased by increasing the z value.

  In addition, as materials of the outer rings 11 and 21 and the inner rings 12 and 22 in the above embodiment, for example, high carbon chromium bearing steel such as JIS standard SUJ2, alloy steel for machine structure such as SCM420, carbon steel for machine structure such as S53C, and the like. Steel such as can be adopted.

  In the above embodiment, the thrust angular ball bearing, which is the rolling bearing for ball screw support of the present invention, is adopted for the fixed side support unit, and the deep groove ball bearing is adopted for the support side support unit. The type of bearing to be used is not limited to this, and other types of rolling bearings may be employed. Further, in the ball screw supporting rolling bearing of the present invention, a seal member that closes both axial ends of the inner ring and the outer ring is disposed, and a urea-based thickener is placed in a space closed by the seal member, the inner ring, and the outer ring. You may enclose the grease containing. Thereby, the durability of the ball screw supporting rolling bearing of the present invention can be further improved. Further, in the above embodiment, the case where the outer ring and the inner ring are employed as the race members of the ball screw supporting rolling bearing of the present invention has been described. However, the race member is configured so that the rolling elements roll on the surface. It may be a member such as a shaft or a housing used. That is, the raceway member should just be a member in which the rolling surface for a rolling element to roll was formed. When the race member is made of steel, a surface modification layer such as a nitride layer formed by nitriding may be formed on the rolling surface of the race member. Thereby, the durability of the ball bearing supporting rolling bearing can be further improved.

  Embodiment 1 of the present invention will be described below. Rolling bearings having rolling elements made of β sialon sintered bodies having various z values were produced, and tests for investigating the relationship between the z value and the rolling fatigue life (durability) were conducted. The test procedure is as follows.

  First, a method for producing a test bearing to be tested will be described. First, β sialon powder prepared by a combustion synthesis method with a z value in the range of 0.1 to 4 is prepared, and is basically the same as the rolling element manufacturing method described in the above embodiment based on FIG. The rolling element whose z value is 0.1-4 by the method was produced. A specific manufacturing method is as follows. First, β sialon powder refined to submicron, aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., AKP30) and yttrium oxide (manufactured by HC Starck Co., Ltd., Yttrium oxide grade C) as a ball mill Were mixed by wet mixing. Then, granulation was performed with a spray dryer to produce granulated powder. The granulated powder was molded into a sphere with a mold and further pressurized by cold isostatic pressing (CIP) to obtain a spherical molded body.

  Subsequently, after performing atmospheric pressure sintering as primary sintering for the molded body, the sintered spheres are obtained by performing HIP (Hot Isostatic Press) in a nitrogen atmosphere at a pressure of 200 MPa. Manufactured. Next, lapping was performed on the sintered spheres to obtain 3/8 inch ceramic spheres (JIS grade G5). And the bearing of the JIS standard 6206 model number was produced in combination with the bearing ring made from bearing steel (JIS standard SUJ2) prepared separately (Example AJ). For comparison, a rolling element made of silicon nitride, that is, a rolling element having a z value of 0 was also produced in the same manner as the rolling element made of β sialon, and similarly assembled to a bearing (Comparative Example A).

Next, test conditions will be described. Maximum contact surface pressure P _max : 3.2 GPa, bearing rotational speed: 2000 rpm, lubrication: circulating oil supply of turbine oil VG68 (clean oil), test temperature: room temperature for the JIS standard 6206 model bearing manufactured as described above A fatigue test was performed under the conditions of The vibration of the bearing during operation is monitored by the vibration detection device, and the test is stopped when the rolling element is damaged and the vibration of the bearing exceeds a predetermined value. Recorded as bearing life. In addition, after the test was stopped, the bearing was disassembled to confirm the damaged state of the rolling elements.

  Table 1 shows the test results of this example. In Table 1, the life in each Example and Comparative Example is expressed as a life ratio with the life in Comparative Example A (silicon nitride) as 1. The damage form is described as “peeling” when peeling occurs on the surface of the rolling element, and “wearing” when the surface is worn without peeling and the test is stopped.

  Referring to Table 1, Examples A to H of the present invention in which the z value is 0.1 or more and 3.5 or less have a life comparable to that of silicon nitride (Comparative Example A). Yes. Further, the form of breakage is “peeling” as in the case of silicon nitride. On the other hand, in Example I in which the z value exceeds 3.5, the life is shortened and wear is observed on the rolling elements. That is, in Example I in which the z value is 3.8, it is considered that although the rolling element finally peeled off, the life of the rolling element was affected by the wear of the rolling element. Furthermore, in Example J in which the z value is 4, the wear of the rolling elements proceeds in a short time, and the durability of the rolling bearing is further reduced.

  As described above, when the z value is in the range of 0.1 to 3.5, the rolling bearing provided with the rolling element made of β sialon sintered body has the durability of the rolling element made of the silicon nitride sintered body. It is almost equivalent to a rolling bearing with On the other hand, if the z value exceeds 3.5, the rolling elements are likely to be worn, resulting in a decrease in the rolling fatigue life. Furthermore, it has been clarified that when the z value increases, the cause of breakage of the rolling element made of β sialon changes from “peeling” to “wear”, and the rolling fatigue life is further reduced. Thus, it was confirmed that a rolling element made of a β sialon sintered body that is inexpensive and excellent in durability can be obtained by setting the z value to 0.1 or more and 3.5 or less.

  In addition, with reference to Table 1, in Example H in which the z value exceeds 3.5, a slight amount of wear has occurred in the rolling elements, and the service life has also decreased compared to Examples A to G. ing. From this, it can be said that the z value is desirably 3 or less in order to ensure sufficient durability more stably.

  From the above experimental results, the z value is preferably 2 or less, and more preferably 1.5 or less, in order to obtain durability (life) equal to or greater than that of a rolling element made of silicon nitride. On the other hand, in view of the ease of production of β sialon powder by a production process employing combustion synthesis, it is preferable to employ a z value of 0.5 or more at which a reaction due to self-heating can be sufficiently expected.

  Embodiment 2 of the present invention will be described below. A test for producing a rolling bearing having rolling elements made of β-sialon sintered bodies having various z values and investigating the relationship between the z value and the rolling fatigue life in an environment in which an impact is applied to the rolling bearing. Was done. The test procedure is as follows.

  First, a method for producing a test bearing to be tested will be described. First, β sialon powder prepared by a combustion synthesis method with a z value in the range of 0.1 to 3.5 is prepared, and the z value is 0.1 to 3.5 by the same method as in Example 1 above. A rolling element was produced. And the bearing of the JIS standard 6206 model number was produced in combination with the bearing ring produced using the various steel materials prepared separately as a raw material (Examples AJ). As steel constituting the race, JIS standards SUJ2, SCM420, SCr420, S53C, S45C, S40C and AISI standard M50 were adopted. For comparison, a rolling element made of silicon nitride, that is, a rolling element having a z value of 0 was also produced in the same manner as the rolling element made of β sialon, and similarly assembled to a bearing (Comparative Example A).

Next, test conditions will be described. For the bearing of the JIS standard 6206 model number manufactured as described above, the maximum contact surface pressure P _max : 2.5 GPa, the bearing rotation speed: 500 rpm, lubrication: turbine oil VG68 circulating oil supply, vibration conditions: 2500 N (50 Hz), Test temperature: An excitation shock fatigue test was performed under the condition of room temperature. The vibration of the bearing during operation is monitored by the vibration detection device, and the test is stopped when the bearing is damaged and the vibration of the bearing exceeds a predetermined value. Recorded as the lifetime of. In addition, after the test was stopped, the bearing was disassembled to confirm the damaged state of the bearing.

  Table 2 shows the test results of this example. In Table 2, the life in each example and comparative example is shown in the upper part of each column as a life ratio with the life of Comparative Example A (silicon nitride) as 1 when the material of the bearing ring is SUJ2. Yes. Moreover, the damaged part (bearing ring or ball) of the bearing is described in the lower part of each column.

  Referring to Table 2, Examples C to H of the present invention having a z value of 0.5 or more and 3.0 or less clearly have a longer life than silicon nitride (Comparative Example A). Yes. Here, as shown in Table 2, the damaged part was a track member (track ring) as in the case of silicon nitride, and the damaged form was delamination. On the other hand, in Examples I and J in which the z value exceeds 3.0, the life is shortened and the rolling element (ball) is damaged (peeled) first. That is, in Example I in which the z value is 3.25, it is considered that the bearing part (ball) made of the β sialon sintered body is damaged due to the impact and the life is shortened. Furthermore, in Example J in which the z value is 3.5, the rolling elements are peeled off in a shorter time, and the durability of the rolling bearing is further reduced.

  On the other hand, in Examples A and B in which the z value is smaller than 0.5, the lifetime is reduced to substantially the same level as in Comparative Example A, and the raceway member is preceded by breakage (peeling). That is, in Example B in which the z value is 0.25, the difference in physical properties from Comparative Example A in which the z value is 0 (silicon nitride) is reduced. Therefore, the collision between the ball made of the β sialon sintered body and the race member facing the ball unilaterally causes damage on the race member side, and the same as Comparative Example A employing the ball made of the silicon nitride sintered body. It is thought that the lifetime was reduced to

  Furthermore, referring to Table 2, even when the z value is 0.5 or more and 3.0 or less, when the hardness (surface hardness) of the opposite bearing ring is less than HV680, The life tends to be shorter than when the hardness is HV680 or higher. This is thought to be because when the hardness of the raceway is low, damage to the raceway member is likely to occur due to the collision between the ball made of β sialon sintered body and the raceway member facing the ball.

  As described above, when the z value exceeds 3.0, the bearing part itself made of the β sialon sintered body is easily damaged, whereas when the z value is less than 0.5, the contact surface pressure between the mating member is low. It increases, and damage to the mating member is likely to occur. And by making z value 0.5 or more and 3.0 or less, the balance of the intensity | strength of the raw material which comprises a rolling element and the reduction of the contact surface pressure between track members is ensured. As a result, it was confirmed that the life of a rolling bearing including a rolling element made of a β sialon sintered body is improved in an environment in which an impact is applied to the bearing. In particular, when the race member is made of steel, the physical properties of the race member and the physical properties of the rolling elements are well matched, and the occurrence of damage due to impact, vibration, or the like can be suppressed. Thus, by setting the z-value of β sialon constituting the rolling element to 0.5 or more and 3.0 or less, it is possible to improve the durability of the ball bearing supporting rolling bearing that may be subjected to an impact load. It was confirmed that there was.

  In addition, when the race member is made of steel, it was confirmed that the surface hardness of the race member is preferably HV680 or more in order to suppress damage to the race member.

  Embodiment 3 of the present invention will be described below. A test was conducted to investigate the formation state of the dense layer and the highly dense layer of the rolling elements made of β sialon constituting the ball screw supporting rolling bearing of the present invention. The test procedure is as follows.

First, a β sialon powder (product name: Melamix, manufactured by Isman Jay Co., Ltd.) having a composition of Si ₅ AlON ₇ prepared by a combustion synthesis method is prepared, and the rolling element described in the above embodiment based on FIG. A cubic test piece having a side of about 10 mm was produced in the same manner as in the manufacturing method. A specific manufacturing method is as follows. First, a β sialon powder refined to submicron, aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., AKP30) and yttrium oxide (manufactured by HC Starck Co., Ltd., Yttrium oxide grade C) as a ball mill Were mixed by wet mixing. Then, granulation was performed with a spray dryer to produce granulated powder. The granulated powder was molded into a predetermined shape with a mold and further pressed by cold isostatic pressing (CIP) to obtain a molded body. Subsequently, the cube test piece was manufactured by heating and sintering the molded body at 1650 ° C. in a nitrogen atmosphere having a pressure of 0.4 MPa (atmospheric pressure sintering).

  Thereafter, the test piece was cut, and the cut surface was lapped with a diamond lapping machine, and then mirror lapping with a chromium oxide lapping machine was performed to form a cross section for observation including the center of the cube. And the said cross section was observed with the oblique light of the optical microscope (the Nikon Corporation make, Microphoto-FXA), and the 50-times-magnification instant photograph (Fujifilm Corporation FP-100B) was image | photographed. Thereafter, the obtained photographic image was taken into a personal computer using a scanner (resolution: 300 DPI). And the binarization process by a brightness | luminance threshold value was performed using the image processing software (Mitani Corporation WinROOF) (binarization separation threshold value in a present Example: 140), and the area ratio of the white area | region was measured.

  Next, test results will be described. FIG. 8 is a photograph of the observation cross section of the test piece taken with an oblique light of an optical microscope. FIG. 9 is an example showing a state in which the image of the photograph of FIG. 8 is binarized by a luminance threshold using image processing software. FIG. 10 shows a region (evaluation region) where image processing is performed when the image of the photograph of FIG. 8 is binarized using a luminance threshold value and the area ratio of the white region is measured using image processing software. FIG. In FIG. 8, the upper side of the photograph is the surface side of the test piece, and the upper end is the surface.

  Referring to FIGS. 8 and 9, the test piece in this example manufactured by the same manufacturing method as that of the above embodiment has a layer with less white area than the inside in the area including the surface. I understand. And, as shown in FIG. 10, the photographed photograph image is divided into three regions according to the distance from the outermost surface of the test piece (region within 150 μm distance from the outermost surface, region within 150 μm and within 500 μm, When the area ratio of the white area was calculated by performing image analysis for each area and obtaining the area ratio of the white area, the results shown in Table 3 were obtained. Table 3 shows the average value and the maximum value of the area ratio of the white area in five fields obtained from five photographs taken at random with each field shown in FIG. 10 as one field of view. Yes.

  Referring to Table 3, the area ratio of the white region in the present example was 18.5% inside, whereas it was 3.7% in the region having a depth of 500 μm or less from the surface. It was 1.2% in the region where the depth from the region was 150 μm or less. From this, in the test piece in the present example produced by the above manufacturing method similar to the above embodiment, a dense layer and a highly dense layer having a white region less than the inside are formed in the region including the surface. It was confirmed.

  Embodiment 4 of the present invention will be described below. A test was conducted to confirm the rolling fatigue life of the rolling element made of the β sialon sintered body constituting the ball bearing supporting rolling bearing of the present invention. The test procedure is as follows.

First, a method for producing a test bearing to be tested will be described. First, a β sialon powder (product name: Melamix, manufactured by Isman Jay Co., Ltd.) having a composition of Si ₅ AlON ₇ prepared by a combustion synthesis method is prepared, and the rolling element described in the above embodiment based on FIG. A 3/8 inch ceramic sphere having a diameter of 9.525 mm was produced in the same manner as the production method described above. A specific manufacturing method is as follows. First, a β sialon powder refined to submicron, aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., AKP30) and yttrium oxide (manufactured by HC Starck Co., Ltd., Yttrium oxide grade C) as a ball mill Were mixed by wet mixing. Then, granulation was performed with a spray dryer to produce granulated powder. The granulated powder was molded into a sphere with a mold, and further pressurized by cold isostatic pressing (CIP) to obtain a spherical molded body.

  Next, the green body is processed so that the processing allowance after sintering becomes a predetermined dimension, and the green body is subsequently heated to 1650 ° C. in a nitrogen atmosphere at a pressure of 0.4 MPa. By sintering, sintered spheres were produced. Next, lapping was performed on the sintered spheres to obtain 3/8 inch ceramic spheres (rolling elements; JIS grade G5). And the bearing of the JIS standard 6206 model number was produced in combination with the bearing ring made from bearing steel (JIS standard SUJ2) prepared separately. Here, the thickness (processing allowance) of the sintered sphere removed by the lapping process on the sintered sphere was changed in eight stages, and eight types of bearings were produced (Examples A to H). On the other hand, for comparison, lapping is performed on sintered spheres (EC 141 manufactured by Nippon Special Ceramics Co., Ltd.) sintered by pressure sintering using raw material powders composed of silicon nitride and a sintering aid in the same manner as described above. Processing was performed, and a bearing of JIS standard 6206 model number was manufactured in combination with a bearing ring (JIS standard SUJ2) prepared separately (Comparative Example A). The machining allowance for lapping was 0.25 mm.

Next, test conditions will be described. Maximum contact surface pressure P _max : 3.2 GPa, bearing rotational speed: 2000 rpm, lubrication: circulating oil supply of turbine oil VG68 (clean oil), test temperature: room temperature for the JIS standard 6206 model bearing manufactured as described above A fatigue test was performed under the conditions of The vibration of the bearing during operation is monitored by the vibration detection device, and the test is stopped when the rolling element is damaged and the vibration of the bearing exceeds a predetermined value. Recorded as bearing life. The number of tests was 15 in each of the examples and the comparative examples, and after calculating the L ₁₀ life, the durability was evaluated by the life ratio with respect to Comparative Example A.

  Table 4 shows the test results of this example. Referring to Table 4, it can be said that the life of the bearings of the examples is all good considering the manufacturing cost and the like. The life of the bearings of Examples D to G in which the dense layer remains on the surface of the rolling element by setting the machining allowance to 0.5 mm or less is about 1.5 to 2 times the life of Comparative Example A. It was. Furthermore, the life of the bearings of Examples A to C in which the high-density layer remained on the surface of the rolling element by setting the machining allowance to 0.15 mm or less was about three times the life of Comparative Example A. From this, it was confirmed that the rolling bearing for ball screw support of the present invention is excellent in durability. The rolling bearing for supporting the ball screw has a machining life of the rolling element made of β sialon sintered body of 0.5 mm or less, and the life is improved by leaving a dense layer on the surface, and the machining cost is 0.15 mm or less. As a result, it was found that the lifetime was further improved by leaving the highly dense layer on the surface.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The rolling bearing for ball screw support of the present invention can be applied particularly advantageously to a rolling bearing for ball screw support that requires reduction in the weight of rolling elements and improvement in fretting resistance.

It is a schematic sectional drawing which shows the structure of the table drive device of the machine tool provided with the ball screw support rolling bearing. It is a schematic sectional drawing which expands and shows the stationary side support unit of FIG. It is a schematic sectional drawing which expands and shows the support side support unit of FIG. It is a general | schematic fragmentary sectional view which shows the principal part of a thrust angular contact ball bearing. It is a general | schematic fragmentary sectional view which shows the principal part of a deep groove ball bearing. It is a figure which shows the outline of the manufacturing method of the rolling bearing for ball screw support in one embodiment of this invention. FIG. 7 is a diagram showing an outline of a method of manufacturing a rolling element made of a β sialon sintered body in one embodiment of the present invention. It is the photograph which image | photographed the cross section for observation of a test piece with the oblique light of the optical microscope. It is an example which shows the state which binarized the image of the photograph of FIG. 8 with the brightness | luminance threshold value using image processing software. It is a figure which shows the area | region (evaluation area | region) which performs image processing.

Explanation of symbols

  1 thrust angular contact ball bearing, 2 deep groove ball bearing, 11, 21 outer ring, 11A, 21A outer ring rolling surface, 12, 22 inner ring, 12A, 22A inner ring rolling surface, 13, 23 balls, 13A, 23A ball rolling surface, 13B, 23B Ball dense layer, 13C, 23C inside, 13D, 23D Ball high dense layer, 14, 24 Cage, 81 Sleeve, 82 Lock nut, 83 Housing, 84 Side lid, 85 Seal member, 86 Housing, 90 Table drive Device, 91 Screw shaft, 92 Fixed side support unit, 93 Support side support unit, 94 Base, 95 Ball nut, 96 Bracket, 97 Table.

Claims (12)

A ball screw supporting rolling bearing that rotatably supports a screw shaft constituting a ball screw with respect to a member arranged to face the screw shaft,
A track member;
A rolling element that contacts the raceway member and is disposed on an annular raceway,
The rolling element is a ball screw supporting rolling bearing, wherein the rolling element is made of ceramics capable of suppressing an impact on the raceway member as compared with the case of silicon nitride.   The rolling element for ball screw support according to claim 1, wherein the rolling element is composed of a sintered body mainly composed of β sialon and composed of remaining impurities.   2. The ball screw supporting rolling bearing according to claim 1, wherein the rolling element is composed of a sintered body mainly composed of β sialon and comprising a remaining sintering aid and impurities. The β-sialon _is represented by the composition formula of _{Si 6-Z Al Z O Z} N 8-Z, satisfy 0.1 ≦ z ≦ 3.5, the ball screw support rolling bearing according to claim 2 or 3 . The β-sialon _is represented by the composition formula of _{Si 6-Z Al Z O Z} N 8-Z, satisfy 0.5 ≦ z ≦ 3.0, the ball screw support rolling bearing according to claim 2 or 3 .   The rolling bearing for supporting a ball screw according to any one of claims 1 to 5, wherein the rolling element has a Young's modulus of 180 GPa or more and 270 GPa or less.   The rolling bearing for supporting a ball screw according to any one of claims 1 to 5, wherein the rolling element has a Young's modulus of 220 GPa to 260 GPa. The track member is made of steel,
The ball bearing supporting rolling bearing according to claim 1, wherein the raceway member has a surface hardness of HV680 or more.   9. The rolling element according to claim 1, wherein the rolling element has a dense layer, which is a dense layer than the inside, in a region including a rolling surface that is a surface in contact with the raceway member. Rolling bearings for supporting ball screws as described in 1.   The ball bearing supporting rolling bearing according to claim 9, wherein an area ratio of a white region observed as a white region is 7% or less when a cross section of the dense layer is observed with oblique light of an optical microscope.   11. The ball screw support according to claim 9, wherein a high-density layer that is a layer having a higher density than other areas in the dense layer is formed in a region including the surface of the dense layer. Rolling bearing.   The rolling bearing for supporting a ball screw according to claim 11, wherein the area ratio of the white region observed as a white region is 3.5% or less when the cross section of the highly dense layer is observed with oblique light of an optical microscope. .